Asthma is a disease that makes it difficult to breathe and in many cases can be debilitating. Asthma is generally manifested by (i) bronchoconstriction, (ii) excessive mucus production, and/or (iii) inflammation and swelling of airways that cause widespread but variable airflow obstructions. Asthma can be a chronic disorder often characterized by persistent airway inflammation, but asthma can be further characterized by acute episodes of additional airway narrowing via contraction of hyper-responsive airway smooth muscle tissue.
Conventional pharmacological approaches for managing asthma include: (i) administering anti-inflammatories and long-acting bronchodilators for long-term control, and/or (ii) administering short-acting bronchodilators for management of acute episodes. Both of these pharmacological approaches generally require repeated use of the prescribed drugs at regular intervals throughout long periods of time. However, high doses of corticosteroid anti-inflammatory drugs can have serious side effects that require careful management, and some patients are resistant to steroid treatment even at high doses. As such, effective patient compliance with pharmacologic management and avoiding stimulus that triggers asthma are common barriers to successfully managing asthma.
Asthmatx, Inc. has developed new asthma treatments that involve applying energy to alter properties of the smooth muscle tissue or other tissue (e.g., nerves, mucus glands, epithelium, blood vessels, etc.) of airways in a lung of a patient. Several embodiments of methods and apparatus related to such treatments are disclosed in commonly-assigned U.S. Pat. Nos. 6,411,852, 6,634,363, and 7,027,869; and U.S. Published Application No. US2005/0010270, all of which are incorporated by reference herein in their entirety.
Many embodiments of the foregoing asthma treatments that apply energy to tissue of the airways use catheters that can be passed (e.g., navigated) through the tortuous pathways defined by the lung airways. FIG. 1, for example, illustrates a bronchial tree 90 in which the various bronchioles 92 decrease in size and have many branches 96 as they extend from the right and left bronchi 94. Accordingly, the treatment devices should be configured to treat airways of varying sizes as well as function properly when repeatedly deployed after navigating through the tortuous anatomy.
In a typical application, a first medical practitioner (e.g., a bronchoscopist) navigates a distal portion of a bronchoscope through the tortuous pathways of the lung until the distal tip of the bronchoscope is at a desired region of an airway. A second medical practitioner (e.g., a nurse or medical assistant) in addition to the first practitioner assists in advancing a catheter of a treatment device through a working lumen of the bronchoscope until a distal portion of the catheter projects out from the distal end of the bronchoscope. After positioning the distal portion of the catheter at a desired first airway site, the first or second practitioner uses one hand to hold the catheter in place relative to the bronchoscope while the second practitioner moves the thumb of one or the other free hand to move a slide-type actuator in a distal direction to drive an electrode array distally out of the catheter. The second practitioner continues to move the slide-type actuator in the distal direction to drive a plurality of electrodes outwardly until the electrodes contact the sidewall of the airway at a first contact site. The first or second medical practitioner then operates a switch that activates an energy source to deliver energy to the first contact site for a treatment period.
After terminating the energy delivery, (i) the second practitioner slides the actuator in a proximal direction to contract the electrodes, (ii) the first or second practitioner repositions the catheter axially along the bronchoscope and the airway to a second contact site, and (iii) with the catheter held in place, the second practitioner slides the actuator distally to re-expand the electrodes until they contact the sidewall of the airway at the second contact site. The first or second practitioner then activates the energy supply to deliver energy to the second contact site for another treatment period. This process is repeated several times at 3-30 mm increments throughout several regions of the variable sized airways in a lung of a patient. As such, this process requires good coordination and communication between the first and second practitioners to treat a patient, but even then such communication takes time. A typical treatment protocol for treating the full lung of a patient can accordingly require three 30-60 minute sessions, which often results in practitioner fatigue.
The tortuous configuration of the lung airways also presents other challenges to efficiently delivering energy to the airway tissue. For example, the treatment device should be sufficiently flexible to follow the working lumen of a bronchoscope and help facilitate accurate steering of the bronchoscope, and the treatment device should enable accurate, reliable deployment of the electrodes at the distal end of the catheter. Friction losses along the catheter, however, can restrict expansion/contraction of the electrodes because only a portion of the force from the actuator is transmitted to the electrode array. This can inhibit the electrodes from appropriately (e.g., fully) contacting the sidewall of the airway, which may reduce the efficacy of the treatment. Additionally, friction along the catheter increases the load on the thumb of the second practitioner as the slide-type actuator is repeatedly moved, which may cause fatigue and also may make it difficult to sense when the electrodes engage the variable sized airways.